Electroplating nickel and cobalt with periodic reverse current



May 24, 1949. G. w. JERNSTEDT ET AL 2,470,775

ELECTROPLATING NICKEL AND COBALT WITH PERIODIC REVERSE CURRENT Filed July 9, 1947 3 n n n n v n n I n 2 Cathodic Cathodic Q 0 U u s Q E 21 X-P/ahng Time X-P/afin 77me u I Two Seconds or Less I Two fiecon s or Less I I Y-Dep/afing Time TNESSES: G W J LNVENfTORSd I eor e erns ed an fi g Myron Ceresa Patented May 24, 1949 LECTRCPLATING NICKEL AND COBALT WITH PERIODIC REVERSE CURRENT George W. Jernstedt and Myron Ceresa, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 9, 1947, Serial No. 759,796

7 Claims.

This invention relates to the electro-deposition of nickel, cobalt and alloys with each other by means of a periodically reversed current.

In electrodepositing nickel, cobalt, as well as alloys with each other, it is highly desirable to produce electrodeposits thereof as smooth as possible. and of the maximum brightness. Furthermore, it is desirable to plate nickel and cobalt at high current densities in order to reduce the time of plating or the size of the plating apparatus. Heretofore the plating of nickel and cobalt was carried out at relatively low current densities, ordinarily always below 50 amperes per square foot of surface, since the quality of the nickel or cobalt electrodeposit is unacceptable if plated at higher current densities. Furthermore, it has been necessary to buff and polish nickel electrodeposits for most commercial uses, as for instance where the nickel was to be overplated with chromium or for other applications where bright and smooth decorative deposits were required. Nickel electroplating has required constant maintenance of the plating baths and considerable skill to secure consistently acceptable work.

As is well known to those skilled in the art, the electrodepositing of nickel presents great dimculties where heavy deposits of the order of 0.005" or greater are required. The nickel tends to become rough and dull even with the greatest of care and considerable buffing and polishing must be subsequently applied to the electroplated members to secure commercially acceptable surface appearance in the nickel plate. Members having sharp corners, for example square plates and the like, have required considerable care in locating them in the plating bath with respect to anodes and the use of quite low current density current is required in order to prevent excessive build up at the corners.

While nickel has been plated from nickel electrolytes containing brighteners, usually organic addition agents, and the deposits are bright, the operation is quite critical. A definite maximum allowable current density at any area being plated cannot be exceeded without burning. The bath composition must be maintained closely. A

drawback to bright nickel. produced in such baths is its brittleness. When wire coated with several thousandths of an inch of this type of bright nickel is flexed, the nickel plate often cracks.

Similar difliculties have been encountered with cobalt as with nickel.

2 trolyte thereof by employing periodic reverse current.

A further object of this invention is to produce bright ductile electrodeposits of nickel, cobalt and alloys with each other directly from an electrolyte thereof by employing periodic reverse current.

A still further object of this inventio is to provide a process of the electrodepositing nickel, cobalt or alloys with each other from an electrolyte thereof which comprises applying to the member being plated a periodic reverse current of such a cycle that the cathodic portion of the cycle is two seconds or less in duration and the anodic current portion of the cycle is of a duration of from to /25 of the cathodic current portion.

Other objects of the invention will in part be obvious and will in part appear hereinafter. For a better understanding of the nature and objects of the invention, reference should be had to the following detailed description and drawing, in which:

Figure 1 is a view in elevation partly in section of an electroplating tank operating in accordance with the invention, and

Fig. 2 is a diagrammatic representation of the periodic reverse current cycle of this invention.

Ithas been discovered that nickel, cobalt and alloys with each other, may be electroplated on members from an electrolyte containing nickel, cobalt or both with a remarkable increase in brightness, speed of plating and smoothness of electrodeposits by applying to the member being plated a periodically reversed current consisting of a series of successive cycles, of which each cycle first renders the member being plated cathodic for a period of time of not more than two seconds to electrodeposit a microscopic increment of metal on the member and then renders the member anodic for a period of time of from to /25 of the cathodic period to deplate a portion of the previously deposited metal increment, the

The object of the present invention isto pro- A vide for expediting the electrodeposition of nickel, cobalt and alloys with each other from an elecanodic period being of such duration and the current density being of such an extent that there is applied to the member coulombs of anodic electrical current corresponding to from 4% to 60% of the coulombs of currents applied during the preceding cathodic period. The most unexpected and improved results have been obtained by employing a periodic reverse current cycle of this nature in electroplating nickel. Where 50 amperes per square foot was previously regarded as maximum current density for plating nearly all types of base members with nickel or cobalt or their alloys by means of continuous direct current,

- produced that were brighter over the entire panel;

the maximum current density being over 300 I amperes per square foot in such panels. Nickel plated work produced by periodic reversed current plating has been exceptionally smooth and free from nodules, burrs, pores, fogging, burning, and pitting as well as other plating defects. Other advantages of the periodic reverse current cycle applied to nickel plating will be set forth hereinafter.

Nickel-containing electrolytes suitable for electroplating nickel may be any acidic nickel salt solutions employed in the art for plating. It has been found that the single or double nickel sulfate and nickel chloride salts alone or in any combination may be employed for electroplating with periodic reverse current. Other platable nickel salts may be employed. The nickel plating baths are acidic, having a pH of from 0.5 to 6. In many cases buiIers, such as boric acid, and other addition agents, may be present; in some case marked beneficial results are obtained when they are present. Examples of suitable addition agents are organicsulfonates, such as naphthalene-1,5-disulfonic acid, ammonium sulfate, formaldehyde, nickel formate, sodium sulfate, sodium lauryl sulfate, and ammonium chloride. Gum arabic and gum tragacanth and the like may be present. If required, additions of hydrochloric or sulfuric acid may be made to the electrolytes.

For plating cobalt, the electrolyte may contain cobalt sulfate, cobalt chloride or mixtures thereof. Similar addition agents to those used with nickel electrolytes may be added to these solutions to advantage. The pH of the aqueous electrolytes may be from 0.5 to 6.

In plating nickel-cobalt alloys, mixtures of nickel salts and cobalt salts are dissolved in the aqueous electrolyte. The baths have a pH range of from 0.5 to 6. For alloy platin cobalt-nickel anodes are used. Particularly useful alloys are those containing irom 80% to 97% nickel by weight and 20% to 3% cobalt by weight. However alloys containing greater amounts of cobalt may be readily plated.

Referring to Fig. 1 of the drawing there is illustrated a nickel or cobalt or alloy electroplating cell I consisting of a tank l2 which may be provided if required, with an insulating and corrosion resistant liner H of synthetic rubber, glass or the like. Disposed within the tank [2 is an aqueous electrolyte [6. A nickel, cobalt or nickel-cobalt alloy anode I8 is disposed in the electrolyte I6. The anode 18 may contain small amounts of common impurities, or be prepared in any desired or conventional way. The anode I8 is supported by a conductor bar 20. A member 22 to be plated with metal is supported by a hanger 24 depending from a conductor bar 26. The member 22 to beplated with nickel may be a metal body or may be prepared from any suitable electrically conducting material capable of being electroplated. Thus it may be of graphite or it may be a wax or plastic body having a surface coated with silver, 9. graphitic, metallic or other electrically conducting material to enable electroplating to be carried out on the surface thereof.

Current is supplied to the conductor bar 20 and 26 by leads 30 from a suitable source 28 of periodically reversed current. The particular mechanism for supplying the periodically reversed current forms no part of the present invention, but suitable means to accomplish periodic current reversal will be obvious to those skilled in the art. Thus directcurrent from a source such as a rectifier, generator or a battery may be periodically reversed by a doublethrow reversing switch operated by hand or by a suitable mechanism. Drum contacts operated by a motor or other timed driving means may be constructed and arranged so that direct current flowing in one direction is applied for a period to the conductor bars 20 and 2B and then reversed, in accordance with the present iiivention. If desired, an electrical generator may be constructed so that its field is reversed at intervals, thereby producing the periodically reversed current or else the windings of an alternating current generator may be so arranged that a periodically reversed current of the type described is generated.

In the copending patent application of'G. W. Jernstedt, Serial No. 610,107, filed August 10, 1945, now Patent 2,451,341, granted Oct. 12, 1948, there is disclosed a periodic reverse current cycle having a cathodic period of from 2 to 40 seconds and an anodic period of from /2 to 10 seconds, which has been found useful for plating a great variety of metals including copper, brass, gold and the like. Some benefits have been secured in plating nickel and cobalt and their alloys with the cycle disclosed in that application. However, we have discovered in accordance with the present invention, that a periodic reverse current in which the cathodic portion of the cycle applied to the member being plated with nickel is two seconds or less and preferably less than /2 second will produce unexpectedly improved, highly polished, smooth nickel, cobalt and nickel-cobalt alloy electrodeposits. In

most cases the electrodeposits will be mirrorlike. The anodic portion of the cycle should be from to /25 of the cathodic portion of the cycle and the current densities adjusted so that the anodic portion of the cycle applies from 4% to 60% of the'coulombs of current applied during the cathodic portion cycle.

The periodic reverse current cycle of this invention is illustrated in Fig. 2 of the drawing. Current is initiall applied to the member 22 rising from 0 to a current value A and rendering the member cathodic for a time interval X of one second or less to the point B where the current is reversed and the member is rendered anodic at a current density value C. During the time interval X, a microscopic increment of nickel, for example, is plated on the member. At C, the nickel increment is partly deplated to remove inferior and unsound nickel during the time interval Y which is from to /25 of the time interval X. At D the current is reversed and the current density passes through a zero value at E and the member is again rendered cathodic at a current density F. The cycle is repeated until a predetermined thickness of nickel is electrodeposited on the member.

While the current from A to B is shown as a steady or constant value, it need not be as uniform or steady as shown. may be rippled or uneven between A and B, and between C and D, or have any selected or unavoidable fluctuations. Also the current may take an appreciable time to rise from to A; likewise from B to C the reversal of the current may take an appreciable length of time so that the lines 0A and 3-0 slope or even dwell at the 0 axis. Thus, in one case, where the anode interval at the 0 axis was /500 of a second, oscillographsshowed actual current flowing in the member for about 0.001 second. The critical factor is that nickel or cobalt .be plated over the interval X and nickel or cobalt be deplated during the interval Y.

While' for practical reasons the current densities at A and C may be substantially the same, it is not necessary that the value 0 be the same as the value A. Good results have been secured where the current density at C has been 2 and 3 times that of the current density at A. The practical limits on the current densities at A and C is that they be not so great that the metal is burned or otherwise harmed. The critical requirement is that the coulombs of current applied during the cathodic portion of the cycle be sufiicient to deposit an increment of metal while the anodic portion of the cycle applies from 4%- to 60% of the coulombs of current applied during the cathodic portion of the cycle to deplate a substantial proportion of the previously plated increment.

When a plating electrical current, constituting the cathode portion of the cycle, is applied to the member being plated, nickel is electrodeposited thereon. Due to many factors entering into the plating out ofnickel, and cobalt, from solution, the metal is ordinarily deposited in disproportionate amounts on the various portions of the member. Sharp corners or other projections, in general, build up nickel, or cobalt thereon much faster than a fiat section. Conversely recesses usually build up the least nickel or cobalt deposits. In some places deposits are produced in a rougher condition than at others. Further as plating progresses, more and more roughness is evident, also nodules and projections grow at accelerated rates. Factors leading to adverse nickel and cobalt plating become more pronounced at higher plating current densities.

During the deplating or anodic portion of the cycle, inferior metal is believed to be preferentially removed from the previously plated increment; for example, nodules, .burrs, and rough projections appear to be removed or deplated substantially more than other portions. A smoothening effect is thus produced. The net result of a complete cycle is that an increment of sound, bright nickel or cobalt or nickel-cobalt alloy is produced. On repeating the cycle, there is built up an electrodeposit composed of a series of high quality nickel or cobalt increments. However, the increments are all united into a homogeneous, sound plate. The nickel or cobalt plate so produced is of a relatively uniform thickness and conforms closely to the shape of the base member. A further advantage of periodic reverse current plating as disclosed herein is that a relatively rough base member may be plated to produce an electrodeposit smoother than itself. While the periodic reverse current cycle of Fig. 2 appears to be relatively inefficient due to the fact that plated metal is anodically removed, thereby requiring a proportionate increase in wattage of current and in the overall time to Thus the current odic reverse current plating to be much more emcient than as calculated. Thus the experience has been that the nickel removed during the anodic portion. of the cycle is readily replatedback so that the emciency of the cathodic cycle is and in some cases the amount of metal plated appears to have been in excess of 100% efiiciency for the net coulombs of cathodic cur-- rent applied. This result is not explainable but constitutes one of 'the advantages of the reverse current plating cycle of this invention. This factor combined with the extraordinarily high current densities usable with periodic reverse current enables a given thickness of metal to be applied in a shorter overall time than with any continuous direct current process known.

Many desirable and unexpected results have been obtainedby electrodepositing nickel on a base member using the periodic reverse current cycle of this invention. The time required to plate a given thickness of nickel has been greatly reduced as compared to any known nickel plating process now employed for depositing nickel by continuous direct current. Times to deposit a given thickness of nickel have been reduced to as little as 20% of the best continuous direct current plating times. This saving in time, while important, isaccompanied by a. great improvement in the quality of the nickel electrodeposited. The surface of the electrodeposits are much brighter and. in many cases, are mirror bright. The surface of the nickel is extremely smooth without nodules, burrs or undesirable nickel build-up on corners, edges and the like. The nickel so electrodeposited appears to be superior in protective value and corrosion resistance as compared to nickel deposited by any known continuous direct current commercial process. The nickel deposits produced by periodic reversed current are usually suitable for the electrodeposition of chromium directly thereupon without any intervening bufling or polishing. It will be appreciated, however, that in many cases the speed of nickel electroplating may be greatly increased with some moderate sacrifice in brilliancy .of the nickel electrodeposit.

Similar benefits have been found in plating cobalt and nickel-cobalt alloys.

It has been found that the time X during which the member being plated with nickel or cobalt or nickel-cobalt alloy is cathodic may be reduced to a small fraction of a second with considerable benefits. When the time X is reduced to from /5 of a second to A00 of a second, optimum plating is secured from many electrolytes. For example, certain nickel electrolyte compositions that do not produce satisfactory nickel plating with continuous direct current under any plating conditions have produced particularly bright and smooth nickel electroplates when the periodic reverse current cycle is such that the cathodic time X is /25 of a second and ess.

It should be understood that when maximum current density values are given for continuous direct current plating of nickel or cobalt herein, these values represent those with which commercially acceptable plating can be produced on most conventional members. Some members have such shapes that they cannot be plated successfully at such high current densities with continuous direct current, but must be plated at.

considerably lower current densities. Since peri- 7 odic reverse current is so much more adaptable and is not as responsive to changes in member shape, it may be employed at the high current densities even for shapes that are difficult to plate by direct current.

The following examples illustrate the practice of the invention.

Example I An aqueous electrolyte was prepared with the following:

Grams/litre Nickel sulfate (NISO4.6H2O) 200 Nickel chloride (NiCl26H2O) 175 Boric acid 40 The composition had a pH of 1.5. The temperature of the electrolyte was about 115 F. Rectangular brass plates approximately square foot in total surface area were plated in this electrolyte using a periodic reverse current having a cathodic time of second and anodic time of & second. Smooth, bright deposits of nickel were produced up to current densities of 150 amperes/square foot, the anodic and cathodic current densities being equal. The rate of nickel deposition was more than twice that using continuous direct current of 50 amperes/square foot, the maximum usable with the bath.

Example II A bath composition was prepared from:

Ounces per gallon Nickel sulfate (hexahydrate) 25 to 55 Nickel chloride (hexahydrate) 6.1-.0 25 Boric acid 5 to 5 The pH of the baths was from 3 to 4.3. The temperature was varied from 115 F. to 140 F. Rectangular brass plates of 6 square foot total surface area were plated in baths having the above composition using a periodic reverse current cycle in which the cathodic portion was /5 second and anodic V25 second. Smooth, bright electrodeposits of nickel were obtained using currents of up to 150 amperes per square foot during the anodic and cathodic portions of the: cycle.

Example III A bath was prepared from:

Ounces per gallon Nickel sulfate (hexanhydrate) 32 Boric acid 4 Cobalt sulfate 1 Ammonium sulfate 0,1 Formaldehyde .33 Nickel formate 6 The pH of the bath could be varied over the range of 2.3 to 3.7 and the temperature varied from 140 F. to 160 F. The anodes consisted of approximately 95% nickel and 5% cobalt. This bath using continuous direct current is not recommended for plating at current densities above amperes per square foot. Employing a periodic reverse current cycle with a cathodic period of one second and an anodic period of /5 second, nickel-cobalt alloy plate was deposited on base members at cathodic current densities of up to 150 amperes per square foot. The nickelcobalt alloy plate was far brighter and smoother than that attainable with continuous direct current at any current density.

The alloy composition, using the bath of Example III, was plated by employing a periodic reverse current cycle having a cathodic portion in which the time duration was V second and the anodic portion was /25 second. The plat- Example IV A bath was prepared by dissolving in water nickel choloride (hexahydrate)--40 ounces per gallonand boric acid4 ounces per gallon. The

pH of the bath was 2. The temperature of the bath was maintained at F. while plating nickel therefrom using a periodic reverse current cycle having a cathodic time of second and an anodic time of /25 second. This bath when employed with continuous direct current produces a dull semi-hard nickel plate. Current densities commercially employed with this bath are from 20 to 100 amperes per square foot with continuous direct current. Employing periodic reverse current bright smooth plates were deposited upon rectangular brass plates 3 /2 by 2" in size at current densities up to 300 amperes per square foot for both cathodic and anodic portions of the cycle. The nickel was smooth and relatively bright throughout this range of current densities. Nickel plate of this character could not be produced under any known conditions using continuous direct current with this bath composition.

Example V An all sulfate nickel electrolyte was prepared hydrate)40 ounces per ga1lon-and boric acid 4 ounces per gallon. Using continuous direct current the nickel plate produced under any known condition was rough and commercially unacceptable. Periodic reverse current employed with this composition produced electrodeposits that were very bright and smooth at current densities of amperes per square foot and higher. A periodic reverse current cycle having a cathodic period of second and an anodic period of /25 second produced an extremely bright electrodeposit at current densities of 150 amperes per square foot for both portions of the cycle. With decreased cathodic and anodic time periods higher current densities of up to 250 amperes per square foot produced good bright nickel plate.

Ewample VI An electrolyte was produced in dissolving in water: I

Ounces per gallon Nickel chloride (hexahydrate) 40 Nickel sulfate (hexahydrate) 8 Boric acid 4 Cathodic Anodic Period Period Seconds Seconds $6 365 $25 5425 3 0 )to ito W250 F20 M 00 Members were plated with several of the above periodic reverse current cycles for hour. The

current employed. No reason is known for this.

unusual efiiciency. Possibly the nickel deplated during the anodic portion of the cycle remains so close to the member being plated that it will replate on cathodic current being applied due to its proximity to the member with substantially no efiective electrical current being required to accomplish the electrodeposition.

Example VII A nickel electrolyte was prepared by dissolving in water the following:

Ounces per gallon Nickel sulfate (hexahydrate) 32 Nickel chloride (hexahydrate); 6 Boric acid 4 The pH of the bath was varied in a range of from 1.5 to 5.6 by adding acid thereto. The temperature was varied from 100 F, to 130 F. The following periodic reverse current cycles were employed:

Cathodic Anodic Period Period Seconds Seconds ment in the plating. However, for all practical purposes the use of anodic and cathodic current densities of the same value was found to be quite satisfactory.

Example VIII An aqueous electrolyte was prepared to contain Ounces per gallon- Cobalt chloride (hexahydrate) 58 Boric acid 6 The cobalt was plated from the electrolyte with the following periodic reverse current cycles:

Cathodic Anodic Period Period Seconds Seconds Mirror bright deposits were secured at current densities of up to 60 amperes per square foot using the above cycles.

In all of the above examples, the voltage varied from 1 to 3 volts. Obviously the voltage may be arranged to produce the particular current density desired.

10 The above examples are not exhaustive of the nickel and cobalt and alloy plating electrolytes that could be employed, but simply indicate the fact that periodic reverse current plating, as disclosed herein, can be applied to a wide variety of nickel and cobalt electrolytes with good results.

Furthermore, the periodic reverse current cyclesgiven are only examples indicative of the practice of the invention. The cycles may be reduced in time to as little as of a second cathodic period and /500 second anodic period with benefit,

Below a period of about /500 second, the anodic current does not deplate metaleflfectively and such short time reverse current cycles do not function to give the advantages of the invention.

The electrolytes may be agitated or stirred with advantage while plating with periodic reverse current. Alsoflltering, preferably continuously, is recommended to secure the smoothest plated work. v

The preparation of the base members to be plated with periodic reverse current may include brushing, degreasing, grinding, sandblasting, anodic cleaning and the like. It should be such as to produce chemically clean surfaces as is conventional.

Nearly all metals may be readily plated with nickel or cobalt by the periodic reverse current of this invention. Brass, copper, iron, steel, zinc, tin, cadmium, gold, silver, nickel and the ike, either solid or plated or coated in any desired manner on a base may be nickel plated with periodic reverse current applied thereto. Thus an initial electrodeposit of nickel or other metal by continuous direct current may be overplated with nickel or cobalt applied by means of periodic reverse current.

Nickel, cobalt and nickel-cobalt alloys electrodeposited as disclosed herein may be subsequently plated with other metals. The high quality electrodeposits produced by this invention will provide improved corrosion resistance, a better base for the later applied metal and other advantages.

It is intended that all matter contained in the above. description and in the accompanying drawlimiting.

We claim as our invention:

1. In the process of electroplating nickel, cobalt and nickel-cobalt alloys on a member from an electroplating electrolyte thereof, the steps comprising applying to the member, while in contact with the electrolyte, a periodically reversed electrical current consisting of successive cycles, of which each cycle renders the member cathodic for a period of time of less than two seonds to electrodeposit an increment of metal on the member and then renders the member anodic for a period of time of from /2 to /25 of the cathodic time period to deplate the metal, the anodic period being not less than /500 of a second, the current density during the anodic period being substantially equal to the current density applied during the cathodic period.

2. ,In the process of electroplating nickel cobalt and nickel-cobalt alloys on a member from an electroplating electrolyte thereof, the steps comprising applying to the member, while in contact with the electrolyte, a periodically reversed electrical current consisting of successive cycles, of which each cycle renders the member cathodic for a period of time of less than two seconds to electrodeposit an increment of the metal on the member and then renders the member anodic for time period to deplate part of the metal increment, the anodic period being not less than /500 of a second, the current density during the anodic period being suilicient to apply from 4% to 60% of the coulombs of current applied during the preceding cathodic period.

3. In the process of electroplating bright deposits of a metal selected from the group consisting of nickel, cobalt and nickel-cobalt alloys on a member from an aqueous electroplating electrolyte containing the metal and having a pH of not more than 6, the steps comprising contacting the member with the electrolyte and applying to the member an electrical current, the electrical current being periodically reversed to render the member cathodic for a period of time of no longer than one-half second to electrodeposit an increment of metal thereon, and then to render the current anodic between successive cathodic periods for a period of time equal to about one-fifth the cathodic time period to deplate metal, the anodic period being not less than /500 of a second, the current density on the member being substantially the same during the anodic and cathodic periods.

4. In the process of electroplating bright deposits of nickel on a member from an aqueous nickel electroplating electrolyte having a pH from 0.5 to 6, the steps comprising contacting the member with the electrolyte and passing an electrical current through the member and electrolyte, the electrical current being periodically re versed whereby to render the member cathodic for a time period of not over one-half second to electrodeposit an increment of nickel on the base member and to render the base member anodic betweensuccessive cathodic periods for a period of time of from to of the preceding cathodic period, the anodic period being more than /500 of a second, the current density being sufficient during the anodic period to deplate a substantial portion of the previously plated increment.

5. In the process of electroplating bright deposits of a metal from the group consisting of nickel, cobalt and nickel-cobalt alloys on a member from an aqueous electroplating electrolyte having a pH of from 0.5 to 6, the steps comprising contacting the member with the electrolyte and passing an electrical current through the member and electrolyte, the electrical current being periodically reversed whereby to render the member cathodic for a time period of not over one-half second to electrodeposit an increment of the metal on the base member and to render the base member anodic between successive cathodic periods for a period of time of from to /25 of Number period.

12 the preceding cathodic period, the anodic period being not less than /500 of a second, the current density being sufllcient during the anodic period to apply from 4% to of the coulombs of current applied during the preceding cathodic 6. In the process of electroplating nickel on a member the steps comprising applying to the member an aqueous electroplating electrolyte comprising a nickel salt solute selected from at least one of the group consisting of nickel sulfate and nickel chloride, the pH of the electrolyte being from 0.5 to 6, passing a periodically reversed electrical current through the member and the electrolyte, the current being alternately anodic and cathodic, the cathodic current periods being from 1 second to has second during which time interval an increment of nickel is electrodeposited on the member and the anodic current period being from to /25 the cathodic time interval, the anodic period being not less than /500 of a second, the current density of each anodic period being sufficient to apply from 4% to 60% of the coulombs of current applied during the cathodic period.

7. In the process of electroplating on a member nickel from aqueous electroplating electrolytes containing nickel, the step comprising passing a periodically reversed electrical current through the member while in contact with the electrolyte, the periodically reversed electrical current composed of a succession of cycles composed of portions first rendering the member cathodic for a period of time from 2 seconds to 0.01 second to plate nickel on the member and then rendering the member anodic for a period of time of from 1 second to /500 second to deplate nickel, the current density being proportional to provide during the anodic portion from 4% to 60% of the coulombs of current applied during the cathodic portion of the cycle.

GEORGE W. JERNSTEDT. MYRON CERESA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Gillis Mar. 26, 1918 Holt Apr. 21, 1925 Pedersen Feb. 23, 1926 FOREIGN PATENTS Number 

